Rearranged evolution table; added new B/W evolutions. #378

There are now (well, have been for a while) multiple ways to evolve
a Pokémon from its unique parent, so the current schema wasn't working.
The parent Pokémon has moved back to the main pokemon table, and
pokemon_evolution has grown an artificial primary key.

New evolution methods for Milotic, Leafeon, Glaceon, Magnezone, and
Probopass have been added.